Method of installing support tendons

ABSTRACT

A method of installing support tendons in clay soil by thermally hardening a mass of clay soil and by anchoring the tendons in the hardened mass.

United States Patent [1 1 Schnabel, Jr.

[111 3,807,182 [4 1 Apr. 30, 1974 METHOD OF INSTALLING SUPPORT TENDONS[76] Inventor: Harry Schnabel, Jr., 7010 Longwqod Dr., Bethesda, Md.20034 [22] Filed: May 3, 1972 [21] Appl. No.1 249,779

[52 us. CI. 61/35, 61/36 A, 6l/53.54, (Sl /53.62 [51] Int. Cl 1302:!5/74 [58] Field of Search 61/36 A, 35, 39, 53.54,

[56] References Cited UNITED STATES PATENTS 3,436,923 4/1969 Lagerstrom61/39 I/ Q, 1 I. /1. I 11-0044 1. lulu L! 3/1941 Ackley 61/36 2,235,6952,514,509 7/1950 O'NeaL. 61/36 A l/l966 White FOREIGN PATENTS ORAPPLICATIONS 609,386 9/1960 Italy 61/36 A Primary Examiner.la cobShapiro Attorney, Agent, or F irmSchuyler, Birch, Swindler, MqK sz lec qt 57 ABSTRACT A method of installing support tendons in clay soil bythermally hardening a mass of clay soil and by anchoring the tendons inthe hardened mass. I

19 Claims, 8 Drawing Figures PATENTEDAPRIBO m4 3L80'IL182 SHEET 1 BF 5,

PATENTEUAPR 30 um SHEEI 2 BF 5 mommmmmiou mmmmao m4 3.807.182

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. 1 METHOD OF INSTALLING SUPPORT TENDONS BACKGROUND OF THE INVENTION Theinstant invention relates to a method of installing and anchoringtendons for supporting structures. The

invention is particularly applicable to the support of sheeting wallsused in building excavations and will therefore be shown and describedin connection with such an excavation. However, the invention is notlimited to sheeting walls and can be employed in connection with variousother applications including, but not limited to, anchoring guy wiresand cable ends of suspension structures and tendons for supportingfoundation structures in tension. The invention is limited,

, sired, and then inserting the tendon with an anchor plate at itsinnermost end into the hole and grouting about the tendon and anchorplate to fill the hole and bond the tendon to thesurr ounding soil.However, in

cohesive soils, generally those comprising substantial proportions ofclay or loess, the use of such-tendon installations has found limitedsuccess due to the low compressive and shear strength of such soils. Theproblem resides in thelow shear strength of such soils,

whereby the anchored tendon tends to pull out of its installed position.

In another field of art, that of constructing building foundationscapable of supporting the compression loads exerted on the earth bylarge structures, a technique has been developed to harden unstableloess soils. This technique is described in papers by I. M. Litvinov,both in Highway Research Board Special Report 60, Soil and FoundationEngineering in the Union of Soviet Socialist Republics, National Academyof Sciences- National Research Council, 1960; and in Volume 96, NumberSM 1, Journal of the Soil Mechanics and Foundations Division, AmericanSociety of Civil Engineers, 1970. Briefly, this hardening techniquereduces the tendency for loess soils to settle when wetted under load,and comprises the steps of boring spaced holes vertically into theearth, inserting a heating means into each bore and then heating thesurrounding earth while the heating means is being withdrawn from thebore. By this technique a column of hardened earth is prepared whichextends, necessarily for foundation construction purposes, from thelowest point of treatment to the surface whereon the foundation is to bebuilt. This technique'has been developed to provide a load-bearingsurface of greater compressive strength, wherein theoretically astructure may be placed on top of such surface with less danger ofdeported by the method of'this invention. In the descrip-. tion theearthen face 1 is discussed as resulting from the structive settling.However, settling still occurs because the clay soil betweenthe-hardened spaced areas retains its weak characteristics, and it isnot practical to harden a sufficient area tobear the substantialcompressive loads of typical buildings.

method of installing support tendons, wherein the advantages found inthe useof such tendons in favorable soil conditions may be obtained inclay bearing soils.

An important object of the invention is to provide a method forsupporting a wall reinforcing an upright earthen face of an excavationor land-fill, which method finds wide application and reduces the costof such an excavation or land-fill.

Briefly, the invention'contemplates a method of improving the tendonanchoring characteristics of a mass of clay soil and emplacing a supporttendon extending from said mass to a structure which requires tensilesupport. Heat is applied to a location in the soil, spaced from thestructure to be reinforced at a temperature andfor sufficient time toharden a mass of the soil around the location of heating. A supporttendon is then anchored to this hardened mass of soil and to thestructure thus providing a tensile support for the struc- .ture.Preferably the heating is achieved by the local ap- BRIEF DESCRIPTION OFTHE DRAWINGS The invention having been generally described, a specificembodiment will be discussed in detail with reference to theaccompanying drawings in which:

FIG. 1 is a side sectional view of a sheeting wall supporting anearthenface into which a casing is being driven.

. FIG. 2 is'a fragmentary top sectional view showing the apparatus forproviding pressurized fuel and air to the burners, the casing and burnerextracting mechanism, and illustrating one embodiment of the subjectmethod.

FIG; 3 is a detail of the burner unit within the casing of FIG; 2.

FIG. 4 is a fragmentary top sectional view showing the insertion of atie-back support tendon through the casing.

FIG. 5 is a fragmentary top sectional view showing the support tendongrouted in place in the hardened soil mass.

FIG. 6 is a side sectional view showing two rows of the. support tendonscompletely installed. r

FIG. 7 is a side sectional view showing the method of this inventionapplied to stabilize and support the foun dation of a radio ortelevision tower or similar structure. Y

FIG. 8 is a side sectional view showing the method of DESCRIPTION OFILLUSTRATIVE EMBODIMENTS As shown in FIG. 1, an earthen face 1 isreinforced by a conventional sheeting wall 2 which is to besupexcavation of the earth 3 on one side of the wall leaving undisturbedearth on the other side of the wall. l-Iowever, the invention is alsoapplicable to an earthen face resulting from a-partial or complete earthfilling on the earth face side of the wall. While only a single tie-backsupport tendon installation willbe described, manifestly a plurality ofsuch installations may, and likely would, be used in a typical sheetingwall nstallation. The term clay soil is used to indicate soil consistingof or containing a substantial proportion of clay or loess or anysimilar substance having the characteristics of clay and hardenable byheat.

Essentially, the earthen face 1 is reinforced by a plu rality ofside-by-side, horizontally spaced, upright soldier piles 4 which maytake the form of l-l-beams. The piles are: conventional and includeflanges 5 to which areaffixed studs 6 for attaching wooden laggingmembers 7. Alternatively, the members 7 may be short sections ofsuitable length for'fitting behind the flanges 5 of adjacent piles 4 inthe well known manner. This wooden lagging 7 supported by the piles 4present a sheeting wall 2 which prevents slippage of the earth from theface 1 into the excavation -3.

' Without reinforcement, the earth 9 behind the face 1 would tend toshear along some inclined plane of slip- I page and fall into theexcavation 3. Although the piles 4 and the lagging members 7 present asheeting wall 2 which bears against the face 1, this wall alone does notprovide adequate support against the horizontal forces produced by theadjacent soil. Therefore the sheeting wall must be further supportedagainst such forces.

The piles 4 are preferably interconnected by one or moreelongated wales10 which extend horizontally of face 1 outside of piles 4. The wales areconstructed of steel or the like andare attached to piles 4 by weldingor other conventional means such as bolts or rivets.

At suitable, horizontally spaced positions along the wale 10 holes 11are provided through both the wale l0 and the lagging members 7 behindthe wale. These holes 11 are of suitable diameter to permit the passagetherethrough of boring casing 12 and its related boring point 13. Thiscasing and its related boring tip 13 are rotatably inserted into theearth 9 by means of boring drive unit 14 carried by a suitableconventional mounting and transporting means 15.

When the casing 12, which, for example, may be a three-inch diameterpipe, has been inserted to a suitable depth, the boring tip 13 isdisengaged by conventional techniques, and the casing 12 is withdrawn ashort distance by a conventional casing puller 16 (FIG. 2). A heatingunit 17 is then inserted into the exposed outer open end of the casing12. One configuration of this heating unit-l7 comprises a burner 17A(FIG. 3) with associated fuel tank 18 and air compressor 19 positionedoutside the exposed upper end 20 of the casing 12. The fuel from thetank 18 is pressured by fuel compressor 21 and is distributed to thevarious treatment locations from manifold 22. The pressurized fuel-airmixture preferably is supplied to the burner unit 17A for burning at alocation adjacent to the innermost end 23 of the casing 12, butalternatively may be burned in a unit at the outer exposed end 20 of thecasing 12 with the hot gases of combustion 24 being conducted by theburner unit 17A tothe innermost end 23 of the casing 12, where they maycontact the surrounding earth. The space between the casing 12 and theburner unit 17 is sealed, such that the pressurized products ofcombustion 24 cannot readily escape up the casing 12 but instead tend tobe forced into thesurrounding earth. Compressed air, preferably inexcess of the requirements for combustion of the fuel and at a pressureabove atmospheric pressure, may be supplied to assist in forcing thesehot gasesinto the soil. A suitable popoff valve or other safety devicemay be installed at the top of the casing to bleed off'excess pressure.Moreover, additional stabilizing chemicals may also be supplied to thearea of soil heating to further treat this area, making it moresusceptible to thermal hardening.

The effect of these hot gases on the clay soil is to hardenandsubstantially increase the compressive and shear strength of asurrounding mass 25 of such soil. The strengthened area extends radiallyoutward from the location at which the heat is applied, and the extentof this strengthened mass is dependent upon the temperature of the gasessupplied and the time duration of the heat treatment. Manifestly, thedegree of strengthening will vary, depending upon the characteristics ofthe soil, and will decrease radially outward from the location of theapplication of the heat, such that the outer portions of thestrengthened mass will blend into the surrounding unaffected soil. Thusthere may be no clearly defined boundary between the strengthened mass25 and'the surrounding soil 26.

While the heatingand strengthening process is in progress, the casing 12and, heating unit 17 may be slowly withdrawn together from the originalfully inserted position. The rate'of suchwithdrawal and the temperatureof the gases 24 are .regulated thus to produce an extended mass 25 oftreated soil, extending radially outward from the point of applicationof the heat and axially with the withdrawal of the heating unit 17 andcasing 12. This mass will be terminated at a point spaced well behindthe face 1.

When the desired mass has been sufficiently treated by this heatingprocess, the heating unit 17 is then removed and the casing 12 isagaininserted substantially to its original emplaced depth. A tendon 27,with its associated earth anchoring means "28, .is then inserted throughthe casing 12 to a position within the strengthened mass (FIG. 4). Thetendon 27 may be a steel rod, cable, or any other well known structure.The casing 12 may then be withdrawn by any conventional means. As thecasing 12 is withdrawn, grout 29 may be inserted through the casing 12around the tendon27 to fill the space between the-tendon 27 and the wall30 of the bore. By grouting as the casing 12 is withdrawn, collapse ofthe wall 30 of the bore is prevented, and this grouting firmly anchorsthe tie-back tendon to the strengthened mass 25 of earth (FIG. 5). Thisstrengthened'mass-of earth, .withits substantially improved compressiveand shear strengths, thus supplies the necessary support for the tensilestresses to be placed upon the tendon 27.

At such time as the grout 29 has hardened and thus firmly anchoredtendon 27 into the earth, the outer end 27A of the tendon 27, whichprotrudes through both the sheeting wall 2 and the support wale 10, maybe secured to the wale .10 by any well' known anchoring means 31 (FIG.6), withor without pre-stressing of the tendon. Thus the tendon 27, intension, provides the lateral support necessary for the sheeting wall 2.

' Whereas a tendon conventionally installed in such a wires or cableends for a suspension structure anchored according to the invention. 7

It is to be understood that the embodiment shown is illustrative of thepresent invention and is not to be a limitation thereof, as otherembodiments and variations will occur to those skilled in the art. Suchvariations may include but are not limited to: use of electricalresistance heating, application of heat to the soil through the walls orthrough perforations in the walls of the casing, and insertion of thetendon without use of the casing and then heating the surrounding soilthrough the surfaces of this tendon. The foregoing and other variationsand substitutions may be made to the specific embodiments disclosedherein without departing from the principles of this invention.Therefore, this invention includes all modifications encompassed withinthe spirit and scope of the following claims.

What is claimed is:

1,. A method of installing support tendons in clay soil comprising thesteps of:

.forming an opening in said clay soil,

applying heat to a location adjacent said opening in said clay soilspaced from the surface of said soil at a temperature and for a timesufficient to harden a mass of said soil around said location,

emplacing a support tendon extending from said surface to said mass andanchoring said tendon to said mass and to a structure spaced from saidlocation.

2. The method of installing supporttendons in clay soil according toclaim 1 wherein said heat is applied by contacting said soil with hotgases at said location.

3. The method of installing support tendons in clay soil according toclaim 2 wherein said hot gases are produced by burning a combustiblemixture at said location.

4. The method of installing support tendons in clay soil according toclaim 2 wherein said hot gases are.

produced by burning a combustible mixture at a position removed fromsaid location and conducting the products of combustion to saidlocation.

5. The method of installing support tendons in clay soil according toclaim 1 further comprising emplacing a casing in said soil, theinnermostiend'of said casing extending at least to the depth ofsaid'location of soil to be treated, said applying heat to said soilbeing from said casing, and said tendon being emplaced through saidcasing.

6. The method of installing support tendons in clay soil according toclaim 5 wherein said heat is applied to said soil by contacting saidsoil with hot gases emanating from said casing.

7. The method of installing support tendons in clay soil according toclaim 6 wherein said hot gases are produced by burning a combustiblemixture within said casing.

8. The method of installing support tendons in clay soil according toclaim 6 wherein said hot gases are produced by burning a combustiblemixture adjacent the inner end of said casing.

9. The method of installing support tendons in clay soil according toclaim 6 wherein said hot gases are produced by burning a combustiblemixture at a position' removed from the interior of said casing and arethen conducted through said casing to said soil.

10. The method of installing support tendons in clay soil according toclaim 5 wherein said heat is applied to said soil while said casing isbeing partially with drawn.

11. The method of installing support tendons in clay soil according toclaim 10 wherein said heat is applied to said soil by contacting saidsoil with hot gases emanating from said casing while said casing isbeing partially withdrawn.

l2. The-method of installing support tendons in clay soil according toclaim 1 wherein the emplacement of said tendons comprises the steps of:

inserting said tendon into said hardened mass, and

grouting between said tendon and said mass.

13. The method of installing support tendons in clay soil according toclaim 12 further comprising the steps:

emplacing a casing into said hardened mass, said inserting of saidtendon being through said casingto the innermost end thereof, and

withdrawing said casing from said' soil.

14. A method of installing support tendons in clay soil located behind awall which reinforces an upright earthen face, and method comprising thesteps of:

forming an opening in said clay soil,

applying heat to a location-adjacent said opening in said clay soilspaced behind said wall at a temperature and for a time sufficient toharden a mass of said 'soil around said location,

emplacing a support tendon extending from said wall 1 to saidmass andanchoring said tendon to said mass and to said wallf 15. The method ofinstalling support tendons in clay soil according to claim 14 whereinsaid heat is applied by contacting said soil with hot gases at saidlocation.

16. The method of installing support tendons in clay soil according toclaim 14 further comprising emplacing a casing in said soil from saidwall, the innermost end of said casing extending at least to the depthof said location of soil to be treated, said applying of heat to saidsoil being from said casing.

17. The method of installing support tendons in clay soil according toclaim 16 wherein said heat is applied to said soil while said casing isbeing partially withdrawn.

18. The method of installing support tendons in clay soil according toclaim 14 wherein the emplacement of said tendons comprises the steps of:v

inserting said tendon into said hardened mass, and

grouting between said tendon and saidmass.

19. The method of installing support tendons in clay soil according toclaim 18 further comprising the steps emplacing a easing into saidhardened mass, said inserting of said tendonbeing through said casing tothe innermost end thereof and withdrawing said casing from said soil.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 807,182 Dated April 30, 1974 lnvent0r(s) Harry Schnabel, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 6, claim 14, line 3 thereof, change "and" to -said-.

Signed and sealed this 10th day of September 1974.

(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM M34050 USCOMM-DC 6O376-P69 a U. 5. GOVERNMENT PRINTINGOFFICE 2 I", 0-366-334.

1. A method of installing support tendons in clay soil comprising thesteps of: forming an opening in said clay soil, applying heat to alocation adjacent said opening in said clay soil spaced from the surfaceof said soil at a temperature and for a time sufficient to harden a massof said soil around said location, emplacing a support tendon extendingfrom said surface to said mass and anchoring said tendon to said massand to a structure spaced from said location.
 2. The method ofinstalling support tendons in clay soil according to claim 1 whereinsaid heat is applied by contacting said soil with hot gases at saidlocation.
 3. The method of installing support tendons in clay soilaccording to claim 2 wherein said hot gases are produced by burning acombustible mixture at said location.
 4. The method of installingsupport tendons in clay soil according to claim 2 wherein said hot gasesare produced by burning a combustible mixture at a position removed fromsaid location and conducting the products of combustion to saidlocation.
 5. The method of installing support tendons in clay soilaccording to claim 1 further comprising emplacing a casing in said soil,the innermost end of said casing extending at least to the depth of saidlocation of soil to be treated, said applying heat to said soil beingfrom said casing, and said tendon being emplaced through said casing. 6.The method of installing support tendons in clay soil according to claim5 wherein said heat is applied to said soil by contacting said soil withhot gases emanating from said casing.
 7. The method of installingsupport tendons in clay soil according to claim 6 wherein said hot gasesare produced by burning a combustible mixture within said casing.
 8. Themethod of installing support tendons in clay soil according to claim 6wherein said hot gases are produced by burning a combustible mixtureadjacent the inner end of said casing.
 9. The method of installingsupport tendons in clay soil according to claim 6 wherein said hot gasesare produced by burning a combustible mixture at a position removed fromthe interior of said casing and are then conducted through said casingto said soil.
 10. The method of installing support tendons in clay soilaccording to claim 5 wherein said heat is applied to said soil whilesaid casing is being partially withdrawn.
 11. The method of installingsupport tendons in clay soil according to claim 10 wherein said heat isapplied to said soil by contacting said soil with hot gases emanatingfrom said casing while said casing is being partially withdrawn.
 12. Themethod of installing support tendons in clay soil according to claim 1wherein the emplacement of said tendons comprises the steps of:inserting said tendon into said hardened mass, and grouting between saidtendon and said mass.
 13. The method of installing support tendons inclay soil according to claim 12 further comprising the steps: emplacinga casing into said hardened mass, said inserting of said tendon beingthrough said casing to the innermost end thereof, and withdrawing saidcasing from said soil.
 14. A method of installing support tendons inclay soil located behind a wall which reinforces an upright earthenface, and method comprising the steps of: forming an opening in saidclay soil, applying heat to a location adjacent said opening in saidclay soil spaced behind said wall at a temperature and for a timesufficient to harden a mass of said soil around said location, emplacinga support tendon extending from said wall to said mass and anchoringsaid tendon to said mass and to said wall.
 15. The method of installingsupport tendons in clay soil according to claim 14 wherein said heat isapplied by contacting said soil with hot gases at said location.
 16. Themethod of installing support tendons in clay soil according to claim 14further comprising emplacing a casing in said soil from said wall, theinnermost end of said casing extending at least to the depth of saidlocation of soil to be treated, said applying of heat to said soil beingfrom said casing.
 17. The method of installing support tendons in claysoil according to claim 16 wherein said heat is applied to said soilwhile said casing is being partially withdrawn.
 18. The method ofinstalling support tendons in clay soil according to claim 14 whereinthe emplacement of said tendons comprises the steps of: inserting saidtendon into said hardened mass, and grouting between said tendon andsaid mass.
 19. The method of installing support tendons in clay soilaccording to claim 18 further comprising the steps of: emplacing acasing into said hardened mass, said inserting of said tendon beingthrough said casing to the innermost end thereof and withdrawing sAidcasing from said soil.